JP2014085579A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce start-up time while suppressing an increase in the size of a fixing unit having external electromagnetic induction heating means.SOLUTION: A fixing device includes: a fixing rotating body that has a heating roller applying heat to a toner image on a recording medium to fuse the toner image; a pressure rotating body that presses the recording medium against the fixing rotating body; and external electromagnetic induction heating means for heating the fixing rotating body. The heating roller includes inside thereof a magnetic flux shielding member and auxiliary heating means facing the external electromagnetic induction heating means.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having these functions. In particular, a toner image is recorded on a plain paper, an OHP film or the like through a process of charging, writing, developing, and transferring. The present invention relates to an image forming apparatus for recording on a material (recording medium). The present invention also relates to a fixing device for fixing a toner image on a recording material through a recording medium between a heated fixing member mounted on an image forming apparatus and a pressure member, and more particularly to an electromagnetic induction heating type fixing device.

  In recent years, from the viewpoint of energy saving, it has become necessary to shorten the rise time by high-speed start-up until the fixing device is ready to pass paper. Therefore, a fixing device in which an IH heater using electromagnetic induction heating, which has higher heat conversion efficiency than conventional halogen heaters, is disposed outside the roller or belt as a heat source has been proposed and used. Further, reducing the heat capacity of the fixing device as much as possible is also taken as an energy saving measure, and the IH fixing device is also reduced in heat capacity.

  However, such a reduction in heat capacity is disadvantageous in terms of fixability, particularly when the fixing device is not sufficiently warmed, such as immediately after startup, and the temperature of the fixing member (roller or belt) surface drops greatly. A typical case of the temperature drop is a case where the heat of the fixing member is taken away by the pressure member or the recording material that has not been sufficiently warmed at the time of continuous paper feeding immediately after rising. In some cases, the minimum fixing temperature is divided by several sheets or several tens of sheets from the start of paper feeding. When the number of sheets to be passed is increased, heat is transmitted from the non-sheet passing range of the fixing member to the pressure member and heated, and as a result, the amount of heat taken away from the fixing member is reduced, so that the fixing property is restored.

  By the way, since an IH heater cannot directly take in a commercial power source due to a configuration using a high frequency, an inverter is used to generate a high frequency. However, when an inverter is created in accordance with the maximum power used for fixing, the inverter is also increased in size, and the coil portion of the IH heater must be increased in size, and the IH heater configuration is increased in size.

  In order to cope with a temperature drop while suppressing an increase in the size of the IH heater configuration, for example, a configuration disclosed in Patent Document 1 can be considered. In the IH fixing belt method, the tension roller in the fixing belt is provided with an auxiliary heat source that compensates for the amount of heat that is insufficient with only the IH heater, which is the main heat source. The same IH heater configuration can be used. However, in such a configuration, the fixing belt is wound around the tension roller in addition to the fixing roller and the heating roller, and the size and heat capacity of the unit are increased accordingly.

  Further, Patent Document 2 discloses that a heater is provided in the pressure roller and the heater is driven by a capacitor as an auxiliary power source in order to suppress the phenomenon of heat escaping to the pressure roller when realizing high-speed startup. Has been. This can also be said to be a configuration that prevents a temperature drop of the fixing belt. However, in this disclosed configuration, since heat is generated from the inside of the pressure roller, it is sufficient to cope with a rapid temperature drop due to continuous paper feeding immediately after the start-up in a device with a quick start-up unless the heat capacity of the pressure roller is reduced. Don't be.

  An object of the present invention is to shorten a rise time while suppressing an increase in the size of a fixing unit having an external electromagnetic induction heating means that is an IH heater.

  The above problems include a fixing rotator having a heating roller that applies heat to a toner image on a recording medium to melt the toner image, a pressure rotator that presses the recording medium against the fixing rotator, and the fixing rotation. A fixing device having an external electromagnetic induction heating means for heating a body, which is solved by providing a magnetic flux blocking member and an auxiliary heating means facing the external electromagnetic induction heating means inside the heating roller.

  According to the present invention, since the magnetic flux blocking member and the auxiliary heating unit facing the external electromagnetic induction heating unit are provided inside the heating roller, the rise time can be shortened while suppressing an increase in the size of the fixing unit. it can.

1 is an overall schematic configuration diagram of a digital copying machine as an image forming apparatus. 1 is an overall schematic configuration diagram of a fixing device installed in an apparatus main body. The difference in edge temperature when the heating roller is a magnetic shunt alloy and when the heat source is a halogen heater with an aluminum material is shown. It is a graph which shows the temperature transition by the presence or absence of an auxiliary heater (whether a capacitor is used as a power source). It is a circuit diagram of an auxiliary heating system by a capacitor in the fixing device according to the present invention. It is a figure explaining the reflective state of the radiant heat of an auxiliary heater. It is a perspective view explaining the reflective process of a magnetic flux shielding board. FIG. 6 is a schematic diagram illustrating another example of a fixing device according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The overall configuration and operation of a digital copying machine as an image forming apparatus will be described with reference to FIG. The apparatus main body 1 of the digital copying machine includes a scanner 50 that optically reads image information of an original, an ADF 10 that continuously conveys the original to the scanner 50, an image forming unit 51, and a paper feeding unit 11 that accommodates a sheet as a recording medium. Is provided. However, its basic configuration is well known, so only a brief description will be given.

  Since the image forming unit 51 corresponds to a color image, the image forming unit 51 is divided into a black image forming unit 51BK, a magenta image forming unit 51M, a yellow image forming unit 51Y, and a cyan image forming unit 51C. Then, exposure light is emitted from the writing unit 59 based on the scanner image information and external image information, respectively. Since the configuration is the same except for the difference in color, only the cyan in the figure is given a reference and will be described below.

  The photosensitive drum 55C irradiated with the cyan exposure light rotates counterclockwise and is charged by the charging unit 57C, and then the drum portion irradiated with the exposure light is attached with toner by the developing unit 56C, and the toner image is formed. It is formed. The toner image is primarily transferred and an image is formed on the intermediate transfer portion 53 by superimposing the respective colors, and the residual toner on the photosensitive drum 55C after the transfer is collected by the cleaning portion 58C.

  The sheet fed from the sheet feeding unit 11 is conveyed to the registration unit 60, skew-corrected by the registration unit 60, and sent to the secondary transfer unit 52 in timing with the toner image of the intermediate transfer unit 53. Then, the toner image is transferred by the secondary transfer unit 52. The sheet after the transfer process reaches the fixing device 20 through the conveyance path. The paper that has reached the fixing device 20 is inserted into a fixing nip between the fixing belt 22 that is a heating rotator and the pressure roller 30 that is a pressure rotator, and heat received from the fixing belt 22 and pressure received from the pressure roller 30. And the toner image is fixed. The paper on which the toner image has been fixed is sent out from the fixing nip and then discharged from the apparatus main body 1 as an output image, completing a series of image forming processes.

  Next, the configuration and operation of the fixing device 20 will be described in detail with reference to FIG. 2 showing the overall schematic configuration of the fixing device 20 installed in the apparatus main body 1. The fixing device 20 mainly includes a fixing roller 21, a fixing belt 22, a heating roller 23, an external induction heating unit 24 of an IH heater, a pressure roller 30, a separation unit 36, and the like.

  Here, an elastic layer such as silicone rubber is formed on the surface of the fixing roller 21, and a pressure roller 30 is pressed to the outer periphery via a fixing belt 22 to form a fixing nip. Then, the pressure roller 30 is rotated counterclockwise in FIG. 2 by a drive unit (not shown), and the fixing roller 21 and the fixing belt 22 are also pressed against each other.

  The fixing belt 22 is a multi-layered endless belt in which an elastic layer and a release layer (surface layer) are sequentially laminated on a base layer made of polyimide resin or the like and having a thickness of 90 μm. It is hung around. In this example, the fixing rotating body is constituted by the fixing belt 22, the heating roller 23, and the fixing roller 21. The elastic layer has a layer thickness of about 200 μm and is made of an elastic material such as silicone rubber, fluorine rubber, or foamable silicone rubber. The release layer has a layer thickness of about 20 μm and is formed of PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. The release layer of the fixing belt 22 ensures the releasability (peelability) for the toner.

  A magnetic shunt alloy is used as a heat generating member for the heating roller 23 to form a magnetic shunt alloy rotating body, which rotates clockwise in FIG. The magnetic shunt alloy is an iron-nickel alloy and loses magnetism when it reaches the Curie temperature. As a result, it has an effect of suppressing heat generation and further increasing the temperature. FIG. 3 shows the difference in end temperature between the case where the heating roller is a magnetic shunt alloy and the case where the heat source is an aluminum material and a halogen heater. When small size paper is passed, in the case of a conventional halogen heater, when the heating roller is a metal such as an aluminum material, the temperature of the non-paper passing portion rises as indicated by a broken line. On the other hand, when the magnetic shunt alloy is heated (heat generation) by the IH heater, magnetism is lost at Kr (Curie temperature), so that heat generation is suppressed and temperature rise of the non-sheet passing portion is suppressed. There is no need to provide extra parts such as a cancel coil.

  Inside the heating roller 23, a magnetic flux shielding plate 40 having a thickness of about 0.4 to 1.6 mm and made of a material having low magnetic permeability such as aluminum or copper is used as a magnetic flux shielding member. It is arrange | positioned in the position facing. The magnetic flux shielding plate 40 keeps a predetermined constant distance from the inner peripheral surface of the heating roller 23. The inner peripheral surface side of the magnetic flux shielding plate 40 is subjected to reflection processing. That is, the inner surface of the magnetic flux shielding plate is coated with a coating such as plating or is mirror-finished. As a result, the radiant heat of the auxiliary heater 41 is reflected as indicated by an arrow in FIG. 6 and heats the one-dot chain line portion a of the heating roller 23. FIG. 7 is a perspective view for explaining the reflection processing of the magnetic flux shielding plate 40.

  If the fixing belt 22 is stretched only by the two axes of the fixing roller 21 and the heating roller 23, the heat capacity can be suppressed as compared with a belt configuration including a tension roller, which is advantageous in shortening the rise time.

  The external induction heating unit 24 includes a coil 25, a core 26, a coil guide 29, and the like, and faces the heating roller 23 via the fixing belt 22 so as to partially surround the heating roller 23. Here, the coil 25 is obtained by extending a litz wire, which is a bundle of fine wires, in the roller axial direction (perpendicular to the paper surface in FIG. 2) so as to cover a part of the fixing belt 22 wound around the heating roller 23. . The coil guide 29 is made of a resin material having high heat resistance and holds the coil 25. The core 26 is made of a material having high magnetic permeability such as ferrite and is disposed so as to face the coil 25 extending in the roller axial direction. The “core part” of the IH heater refers to both opposing core parts that contribute to electromagnetic induction heating. Therefore, the core 26 of the external induction heating unit 24 and the magnetic shunt alloy of the heating roller 23.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on the core metal, and is pressed against the fixing roller 21 via the fixing belt 22. The pressure roller 30 is configured to be pressurized and depressurized, and a cleaning means 33 is in contact with the surface. A halogen heater 35 is provided inside the pressure roller 30, and the temperature is detected by a thermistor 39 disposed facing the outer periphery of the roller, and on / off control is performed.

  Since the paper P is transported to the fixing nip that is a contact portion between the fixing belt 22 and the pressure roller 30, a guide plate for guiding the transport of the paper P is provided on the entrance side of the fixing nip. On the outlet side of the fixing nip, a separation unit 36 is provided that includes a separation plate that guides the conveyance of the sheet P and separates the sheet P from the fixing belt 22.

  Further, an auxiliary heater 41 is disposed inside the heating roller 23. As the auxiliary heater, a halogen heater or a ceramic heater is assumed, but an internal IH heater may be used. There may also be a plurality of auxiliary heaters. As described above, the reflection processing is applied to the inner peripheral surface of the magnetic flux shielding plate 40, so that the radiant heat of the auxiliary heater 41 is reflected by the inner peripheral surface of the magnetic flux reflection plate and the inner periphery of the heating roller on the opposite side. The portion is heated, and the heating roller 23 is efficiently heated in combination with the external induction heating unit 24.

FIG. 4 shows the temperature transition with and without the auxiliary heater 41. The power source of the auxiliary heater 41, which is a halogen heater, is a capacitor (not shown), and power is supplied from the capacitor. The capacitor is charged while the image forming apparatus is operating at less than the maximum power, for example, during standby after starting up, and supplies power to the auxiliary heater 41 by discharging at a predetermined timing. FIG. 4 shows the temperature transition when power is supplied from the capacitor to the auxiliary heater at the same time as the rise and when the auxiliary heater is not provided (including the case where the auxiliary heater is provided but the power source is not a capacitor). Yes. When power is supplied from the capacitor, the rise time is time t1, and when there is no auxiliary heater (when power cannot be supplied to the auxiliary heater), the rise time is time t2, and t1 <t2. It is in. After that, when the continuous paper feeding is performed immediately, the auxiliary heater 41 maintains the fixing lower limit temperature TL or higher by power supplement for time Δt. On the other hand, when there is no auxiliary heater 41 (when electric power cannot be supplied to the auxiliary heater), the temperature of the fixing belt 2 gradually decreases due to continuous paper passing after rising, and the temperature becomes lower than the lower limit fixing temperature _TL , resulting in a cold offset. There is. In other words, by using a capacitor as the power source for the auxiliary heater, it is possible to compensate for the heater power that is limited by the rated power of the machine body at the time of startup, shortening the startup time and reducing the temperature at the beginning of continuous paper feeding. Can be prevented. FIG. 5 is a circuit diagram of an auxiliary heating system using a capacitor in the fixing device according to the present invention.

  Further, a non-contact first temperature detecting means 28 is installed in the vicinity of the induction heating unit 24, and detects the surface temperature (fixing temperature) on the fixing belt 22 wound around the heating roller 23 to thereby detect the IH heater. The temperature is controlled. The second temperature detecting means 42 disposed on the surface of the heating roller 23 inside the fixing belt 22 detects the temperature inside the fixing belt 2 of the heating roller 23 by the auxiliary heater 41. The auxiliary heater 41 is configured so that power is supplied simultaneously with or during the rotation of the heating roller 23 and no power is supplied while the heating roller 23 is stopped. Specifically, a rotation detection member (photo sensor or the like) of the heating roller 23 (not shown) is provided to detect the presence or absence of rotation and to perform control for permitting power supply. By disposing the second temperature detection means 42 on the surface of the heating roller 23 inside the fixing belt 22, the first temperature detection means 28 for the IH heater should be used even if power is supplied during non-rotation. High temperature can be detected independently, ensuring safety.

  The fixing device 20 configured as described above operates as follows. As the pressure roller 30 is driven to rotate, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the heating roller 23 also rotates in the clockwise direction, and the fixing roller 21 also rotates in the direction of the arrow. By passing a high-frequency alternating current through the coil 25, an eddy current is generated on the surface of the heating roller 23, and Joule heat is generated by the electric resistance of the heating roller 23 itself. Due to this Joule heat, the fixing belt 22 wound around the heating roller 23 is heated at a position facing the induction heating unit 24. Also, the heating roller 23 is heated from the inside by the auxiliary heater 41 to heat the fixing belt 22. The fixing belt 22 thus heated reaches the fixing nip. On the other hand, the paper P carrying the toner image T through the image forming process described above is fed into the fixing nip while being guided by the guide plate. In the fixing nip, the toner image T melted by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30 is pressed against the paper P to be fixed, and the paper P is sent out from the fixing nip.

  FIG. 8 shows a fixing device according to the second embodiment. This fixing device is a heat roller type fixing device mainly including a fixing roller 71, an external induction heating unit 74 of an IH heater, a pressure roller 80, a magnetic flux shielding plate 90, and the like. A separation unit is also provided, which is different from the belt-type fixing device shown in FIG. 2 in that it does not have a fixing belt or a heating roller.

  The fixing roller 71 includes a heat generating layer made of a magnetic shunt alloy, an elastic layer made of silicone rubber or the like, a release layer (surface layer) made of fluorine resin or the like. The inside of the fixing roller 71 has a hollow structure, and a magnetic flux shielding plate 90 made of a material with low magnetic permeability such as aluminum or copper is disposed at a position facing the width portion of the external induction heating unit 74. The inner peripheral surface side of the magnetic flux shielding plate 90 is subjected to reflection processing. Further, an auxiliary heater 91 driven by electric power from the capacitor of the auxiliary power supply device is disposed inside the fixing roller 71, and the inner peripheral portion of the fixing roller 73 on the fixing nip side is reflected by the reflection processing of the magnetic flux shielding plate 90. Can be heated.

The external electromagnetic induction heating unit 74 includes a coil 75, a core 76, a coil guide 79, and the like, as in the embodiment of FIG.
A non-contact first temperature detecting means 78 is installed in the vicinity of the induction heating unit 74 to control the IH heater temperature. Further, a second temperature detection unit 92 is disposed at a peripheral position of the fixing roller 73 away from the induction heating unit 74, and the temperature of the heating roller 73 is detected by the auxiliary heater 91. The auxiliary heater 91 operates in the same manner as the auxiliary heater 41 in FIG.

  The pressure roller 80 in which an elastic layer such as fluorine rubber or silicone rubber is formed on the core metal is configured to be able to be pressurized and depressurized, and in the same manner as the embodiment of FIG. A halogen heater 85 driven by the electric power is arranged. The temperature is detected by a thermistor 89 disposed opposite to the outer periphery of the roller, and on / off control is performed.

DESCRIPTION OF SYMBOLS 21 Fixing roller 22 Fixing belt 23 Pressure roller 24 External induction heating part 30 Pressure roller 36 Separation unit 40 Magnetic flux shielding board 41 Auxiliary heater

JP 2009-139664 A JP 2007-79142 A

Claims (8)

  A fixing rotator having a heating roller that applies heat to the toner image on the recording medium to melt the toner image, a pressure rotator that presses the recording medium against the fixing rotator, and heats the fixing rotator. A fixing device having an external electromagnetic induction heating unit, wherein a magnetic flux blocking member and an auxiliary heating unit facing the external electromagnetic induction heating unit are provided inside the heating roller.   The fixing rotator includes the heating roller partially surrounded by the external electromagnetic induction heating means, a fixing belt, and a fixing roller that contacts the pressure rotator through the fixing belt to form a fixing nip. The fixing device according to claim 1, wherein the fixing device is configured.   The fixing device according to claim 1, wherein the fixing rotator is constituted by the heating roller, and the heating roller is in contact with the pressure rotator to form a fixing nip.   The fixing device according to claim 1, wherein the heating roller includes a magnetic shunt alloy rotating body.   The fixing device according to claim 1, wherein a power source of the auxiliary heating unit is a capacitor.   The fixing device according to claim 1, wherein a temperature detection unit is disposed inside the fixing belt and detects the temperature of the auxiliary heating unit.   The fixing device according to claim 1, wherein a reflection process is performed on a side of the magnetic flux blocking member facing the auxiliary heating unit.   An image forming apparatus comprising the fixing device according to claim 1.

Images